Computers, personal computers and the like have recently been remarkably popular and accordingly storage mediums for use therein, especially the capacity of the optical disc has been highly densified more and more, thereby requiring many types thereof.
As for the optical disc, there are, for example, a digital video disc-random access memory, and a digital video disc-random memory (hereinafter referred to as DVD-RAM, DVD-RW and the like, all of which are manufactured by laminating two discs.
Notwithstanding, outstanding performance, for example, not only greater memory capacity but also high capacity of the optical disc which includes a single layered disc (the so-called DVD) is required.
This type of DVR has memory capacity approximately five times as much as the conventional DVD, for example, 22.5 gigabytes.
The optical disc in the form of DVR has been so dimensioned that its thickness is 1.2 mm, external diameter is 120 mm, and the internal diameter of its center hole is 15 mm.
Its sectional configuration is such that an information applied pit is formed on one side of a single layered disc, and that the pit is protected and covered by resin material.
The protective layer is of 0.1 mm and is adapted to read out information applied to the pit by means of a blue laser of a wave length, for example of 405 nanometers.
Now, for manufacturing the optical disc which is formed with the protective layer by means of this type of resin material, there is a method which is composed of the steps of applying ultraviolet light curable resin to the pit surface of the single layered disc, thereafter rotating the single layered disc to develop ultraviolet light curable resin on the surface of the single layered disc, and finally irradiating the ultraviolet light thereto and curing the same.
However, this method when used does not necessarily develop the ultraviolet light curable resin on the single layered disc as a whole evenly.
In this connection, it is noted that this type of DVR requires an extremely uniform protective layer if the aforementioned blue laser is used since the distance to the recording layer is specified as 0.1 mm.
Furthermore, an adhesive may be outwardly scattered at any rate by centrifugal force to cause circumferential stains while being scattered and lost which lowers an effective usage rate.
Still more, means or the like for irradiating the ultraviolet light, i.e. a large scaled device or means for forming the protective layer are required, thereby increasing costs.
In view of the aforementioned, a method for manufacturing DVR is necessitated without requiring a step for developing the adhesive as mentioned hereinbefore.
The present invention is provided to solve the aforementioned problem.
More specifically, it is an object of the present invention to provide a method for manufacturing an optical disc for readily and simply forming a protective layer on the single layered disc.
A further object of the invention is to provide a four layered adhesive sheet member for use as well as a rolled member.
In view of the aforementioned problems, as a result of concentrated research thereon, such problem has been readily and uniformly solved more than as expected by employing an adhesive sheet consisting of a four layered adhesive sheet member.
More specifically, a first aspect of the invention resides in a method for manufacturing an optical disc to allow a protective sheet with an adhesive layer to abut against a single layered adhesive sheet member, and then a protective sheet is bonded to the single layered disc.
A second aspect of the invention resides in the method for manufacturing an optical disc wherein there is provided an elongated release paper, a protective sheet temporarily attached to the elongated release paper, an adhesive layer on the protective sheet, a release paper tacked to the adhesive layer, wherein the release paper is allowed to expose the adhesive layer, a three layered adhesive sheet from which the release sheet is released is adapted to abut against the surface of the single layered disc to transport and bond the surface of the single layered disc, and wherein the elongated release paper is released from the protective sheet bonded to the single layered disc to thereby expose the protective sheet on the single layered disc.
A third aspect of the invention resides in the method for manufacturing an optical disc wherein the adhesive layer is exposed by releasing the release paper from the four layered adhesive sheet composed of an elongated release paper, a protective sheet temporarily attached to the elongated release paper, an adhesive layer on the protective sheet, a release paper temporarily adhered to the adhesive layer, wherein the release paper is released from the four layered adhesive sheet to abut against the surface of the single layered disc to transport and bond the surface of the single layered disc through the adhesive layer, and wherein the elongated release paper is released from the protective sheet bonded to the single layered disc to thereby expose the protective sheet on the single layered disc and thereafter, the single layered disc is pressured by an atmosphere of an air pressure to eliminate air bubble.
A fourth aspect of the invention resides in the method for manufacturing an optical disc wherein the adhesive sheet member is so pressed against the single layered disc as to enlarge the area of contact therebetween from the center to the outside when the three layered adhesive sheet member abuts against the surface of the single layered disc.
A fifth aspect of the invention resides in the method for manufacturing an optical disc wherein the adhesive sheet member is pressed against the single layered disc by a roller when the three layered adhesive sheet member abuts against the surface of the single layered disc.
A sixth aspect of the invention resides in the method for manufacturing an optical disc wherein the protective sheet is formed of polycarbonate resin.
A seventh aspect of the invention resides in the method for manufacturing an optical disc wherein a release paper is polyethylene terephthalate resin as processed by silicone.
A eighth aspect of the invention resides in the method for manufacturing an optical disc wherein an elongated release paper is polyethylene terephthalate resin as processed by silicone.
A ninth aspect of the invention resides in the method for manufacturing an optical disc wherein pneumatic pressure is more than 10 kg/cm3.
A tenth aspect of the invention resides in the four layered adhesive sheet which is employed when the optical disc is manufactured wherein said four layered adhesive sheet member comprises an elongated release paper, a protective sheet adapted to longitudinally, temporarily adhere to the elongated release paper at regular intervals, an adhesive layer formed on the protective sheet, and a release paper adapted to temporarily adhere to the adhesive layer and wherein an opening is bored through the four layered adhesive sheet.
The eleventh feature of the invention resides in a four layered adhesive sheet member wherein the protective sheet is formed of polycarbonate resin whereas the adhesive layer of the protective sheet is formed of acrylic adhesive.
The twelfth feature of the invention resides in the roll member formed by winding the four layered adhesive sheet member used for manufacturing the optical disc into a cylinder in a mandrel form which is employed when the optical disc is manufactured wherein said four layered adhesive sheet member comprises an elongated release paper, a protective sheet adapted to longitudinally, temporarily adhere to the elongated release paper at regular intervals, an adhesive layer formed on the protective sheet, and a release paper adapted to temporarily adhere to the adhesive layer, and wherein an opening is bored through the four layered adhesive sheet.
The thirteenth feature of the invention resides in the rolled member wherein the four layered adhesive sheet member is wound around a mandrel cylinder with a center hole through the non-adhesive attached sheet.
So long as the invention conforms to the aforementioned objects, the invention may be practiced in combination with more than two defined arrangements selected from the aforementioned aspects 1-13.
The specifications of the four layered adhesive sheet member are selected optionally for the desired amount of protective thickness.
By use of the four layered adhesive sheet member, a uniform protective layer may be formed.
The thickness of the protective layer on the single layered optical disc may be readily changed by only changing the thickness of protective sheet 1B, the protective layer may be formed evenly on the surface of the single layered disc without any air bubbles or creases. Due to the use of the four layered adhesive sheet, a more effective optical disc may be possibly obtained.
In other words, different from lamination with a conventional ultraviolet curable resin, this invention does not necessitate the step of developing the adhesive and of irradiating with an ultraviolet beam, thereby curtailing numbers of manufacturing steps or processes.